Rhythmbox is the GNOME-standard audio player, which you can usually take to mean that it is perfectly acceptable at its stated goal, but offers little by way of configuration, and damn little outside its scope.
Rhythmbox, like most of the GTK-based audio players available, is GStreamer-based, and will play whatever GStreamer can decode. Written in C, Rhythmbox is pretty snappy, though it tends to get a bit sluggish on large music collections.
As far as I can remember, Rhythmbox (or possibly Banshee?) was the first to implement the “paned” album browsing concept, where select a top-level item in one pane will narrow down the results in the other pane. This is the only viewing method that Rhythmbox offers, which is fine if it works for you, but not if you prefer an album list, alphabetical breakdown, or even a file view.
Rhythmbox offers basic file properties and tag editing capabilities: title, artist, album, genre, track, disc, and year, and not much else. Some features, such as the rating, allow you to customize your music selection, but it’s an early start at a much-demanded feature that other players are already doing better.
It reports my Bruckner album (which has Composer and Performer tags, but not Artist), as an unknown artist—Rhythmbox has no concept of more esoteric tags.
Album art was added to Rhythmbox quite a long time ago, but it always looks to the internet for its album art, and not for art that’s (a) embedded in the files, or, more commonly, (b) included in the album’s directory as a
folder.jpg or something similar. The downloading mechanism gives no indication as to its status: it either doesn’t do anything, or it will fade in a small thumbnail of the album cover whenever it finally finishes doing its business.
Rhythmbox also offers cursory support for last.fm integration, mobile devices support, and Jamendo (OSS-friendly music store) support.
In Summary: Rhythmbox is, like many OS defaults, a basic program that serves basic needs. However, it tends to fall short at the slightest demand, and its extensibility falls short of other players (not written in C). If you are at all particular about your music collection or listening habits, you’ll want to skip Rhythmbox.